Initial access for reconfigurable intelligent surface assisted communication in the absence of reciprocity

Abstract

Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may receive, from a base station and via a reconfigurable intelligent surface (RIS), a synchronization signal block (SSB) corresponding to a first SSB type configured for RIS-assisted procedures. The UE may select a random access channel (RACH) occasion including multiple physical random access channel (PRACH) transmission slots based at least in part on receiving the SSB corresponding to the first SSB type. The UE may transmit, to the base station, a PRACH communication in the multiple PRACH transmission slots of the RACH occasion. Numerous other aspects are described.

1 . A method of wireless communication performed by a user equipment (UE), comprising:
 receiving, from a base station and via a reconfigurable intelligent surface (RIS), a synchronization signal block (SSB) corresponding to a first SSB type configured for RIS-assisted procedures;   selecting a random access channel (RACH) occasion including multiple physical random access channel (PRACH) transmission slots based at least in part on receiving the SSB corresponding to the first SSB type; and   transmitting, to the base station, a PRACH communication in the multiple PRACH transmission slots of the RACH occasion.   
     
     
         2 . The method of  claim 1 , wherein receiving the SSB corresponding to the first SSB type comprises receiving the SSB reflected by the RIS on a receive beam of the UE, and wherein transmitting the PRACH communication comprises:
 transmitting the PRACH communication in the multiple PRACH transmission slots of the RACH occasion on a transmit beam of the UE that corresponds to the receive beam of the UE that received the SSB.   
     
     
         3 . The method of  claim 1 , wherein transmitting the PRACH communication comprises:
 transmitting, in the multiple PRACH transmission slots of the RACH occasion, the PRACH communication multiple times on each transmit beam of a plurality of transmit beams of the UE.   
     
     
         4 . The method of  claim 3 , further comprising:
 selecting, from the plurality of transmit beams of the UE, a transmit beam for transmitting an uplink communication to the base station based at least in part on a determination of which transmit beam transmits the PRACH communication that is received by the base station.   
     
     
         5 . The method of  claim 1 , further comprising:
 selecting, based at least in part on receiving the SSB corresponding to the first SSB type, a PRACH preamble that indicates a transmit beam of the base station used to transmit the SSB received by the UE and a beam from the RIS that reflected the SSB received by the UE, wherein the PRACH communication includes the PRACH preamble.   
     
     
         6 . The method of  claim 1 , wherein selecting the RACH occasion comprises:
 selecting the RACH occasion to correspond to a transmit beam of the base station used to transmit the SSB received by the UE and a beam from the RIS that reflected the SSB received by the UE.   
     
     
         7 . The method of  claim 1 , wherein selecting the RACH occasion comprises:
 selecting the RACH occasion based at least in part on a mapping between RACH occasions and SSB types.   
     
     
         8 . The method of  claim 7 , wherein the mapping includes a first set of RACH occasions associated with the first SSB type and a second set of RACH occasions associated with a second SSB type configured for non-RIS assisted procedures, and wherein selecting the RACH occasion comprises:
 selecting the RACH occasion from the first set of RACH occasions.   
     
     
         9 . A method of wireless communication performed by a base station, comprising:
 transmitting, on a first transmit beam of the base station, multiple transmissions of a synchronization signal block (SSB) corresponding to a first SSB type configured for reconfigurable intelligent surface (RIS)-assisted procedures;   performing beam sweeping using multiple receive beams of the base station over multiple physical random access channel (PRACH) transmission slots of a random access channel (RACH) occasion associated with the SSB; and   selecting, from the multiple receive beams of the base station, a first receive beam for receiving uplink communications from a user equipment (UE) based on receiving, from the UE and via a RIS, a PRACH communication on the first receive beam during the beam sweeping.   
     
     
         10 . The method of  claim 9 , wherein transmitting the multiple transmissions of the SSB corresponding to the first SSB type comprises:
 transmitting the multiple transmissions of the SSB on the first transmit beam toward the RIS, wherein each of the multiple transmissions of the SSB on the first transmit beam is to be reflected by the RIS using a different beam.   
     
     
         11 . The method of  claim 9 , wherein transmitting the multiple transmissions of the SSB corresponding to the first SSB type comprises:
 transmitting, on each of the first transmit beam and one or more other transmit beams of the base station, multiple transmissions of the SSB corresponding to the first SSB type.   
     
     
         12 . The method of  claim 9 , wherein the PRACH communication includes a PRACH preamble that indicates the first transmit beam of the base station and a beam from the RIS associated with a transmission of the SSB, of the multiple transmissions of the SSB, that is received by the UE. 
     
     
         13 . The method of  claim 9 , wherein the RACH occasion during which the PRACH communication is received corresponds to the first transmit beam of the base station and a beam from the RIS associated with a transmission of the SSB, of the multiple transmissions of the SSB, that is received by the UE. 
     
     
         14 . The method of  claim 9 , wherein the multiple PRACH transmission slots of the RACH occasion are associated with multiple transmissions of the PRACH communication by the UE, and wherein performing beam sweeping using the multiple receive beams of the base station comprises:
 monitoring each of the multiple PRACH transmission slots using a respective receive beam of the multiple receive beams base station to determine whether the PRACH communication is received on the respective receive beam.   
     
     
         15 . The method of  claim 9 , wherein the multiple PRACH transmission slots of the RACH occasion are associated with multiple transmissions of the PRACH communication by the UE and reflected using multiple beams from the RIS. 
     
     
         16 . The method of  claim 9 , wherein the first transmit beam corresponds to a first spatial filter of the base station and the first receive beam corresponds to a second spatial filter of the base station. 
     
     
         17 . A user equipment (UE) for wireless communication, comprising:
 a memory; and   one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:
 receive, from a base station and via a reconfigurable intelligent surface (RIS), a synchronization signal block (SSB) corresponding to a first SSB type configured for RIS-assisted procedures; 
 select a random access channel (RACH) occasion including multiple physical random access channel (PRACH) transmission slots based at least in part on receiving the SSB corresponding to the first SSB type; and 
 transmit, to the base station, a PRACH communication in the multiple PRACH transmission slots of the RACH occasion. 
   
     
     
         18 . The UE of  claim 17 , wherein the one or more processors, when receiving the SSB corresponding to the first SSB type, are configured to receive the SSB reflected by the RIS on a receive beam of the UE, and wherein the one or more processors, when transmitting the PRACH communication, are configured to:
 transmit the PRACH communication in the multiple PRACH transmission slots of the RACH occasion on a transmit beam of the UE that corresponds to the receive beam of the UE that received the SSB.   
     
     
         19 . The UE of  claim 17 , wherein the one or more processors, when transmitting the PRACH communication, are configured to:
 transmit, in the multiple PRACH transmission slots of the RACH occasion, the PRACH communication multiple times on each transmit beam of a plurality of transmit beams of the UE.   
     
     
         20 . The UE of  claim 17 , wherein the one or more processors are further configured to:
 select, based at least in part on receiving the SSB corresponding to the first SSB type, a PRACH preamble that indicates a transmit beam of the base station used to transmit the SSB received by the UE and a beam from the RIS that reflected the SSB received by the UE, wherein the PRACH communication includes the PRACH preamble.   
     
     
         21 . The UE of  claim 17 , wherein the one or more processors, when selecting the RACH occasion, are configured to:
 select the RACH occasion to correspond to a transmit beam of the base station used to transmit the SSB received by the UE and a beam from the RIS that reflected the SSB received by the UE.   
     
     
         22 . The UE of  claim 17 , wherein, the one or more processors, when selecting the RACH occasion, are configured to:
 select the RACH occasion based at least in part on a mapping between RACH occasions and SSB types.   
     
     
         23 . The UE of  claim 22 , wherein the mapping includes a first set of RACH occasions associated with the first SSB type and a second set of RACH occasions associated with a second SSB type configured for non-RIS assisted procedures, and wherein the one or more processors, when selecting the RACH occasion, are configured to:
 select the RACH occasion from the first set of RACH occasions.   
     
     
         24 . A base station for wireless communication, comprising:
 a memory; and   one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:
 transmit, on a first transmit beam of the base station, multiple transmissions of a synchronization signal block (SSB) corresponding to a first SSB type configured for reconfigurable intelligent surface (RIS)-assisted procedures; 
 perform beam sweeping using multiple receive beams of the base station over multiple physical random access channel (PRACH) transmission slots of a random access channel (RACH) occasion associated with the SSB; and 
 select, from the multiple receive beams of the base station, a first receive beam for receiving uplink communications from a user equipment (UE) based on receiving, from the UE and via a RIS, a PRACH communication on the first receive beam during the beam sweeping. 
   
     
     
         25 . The base station of  claim 24 , wherein the one or more processors, when transmitting the multiple transmissions of the SSB corresponding to the first SSB type, are configured to:
 transmit the multiple transmissions of the SSB on the first transmit beam toward the RIS, wherein each of the multiple transmissions of the SSB on the first transmit beam is to be reflected by the RIS using a different beam.   
     
     
         26 . The base station of  claim 24 , wherein the one or more processors, when transmitting the multiple transmissions of the SSB corresponding to the first SSB type, are configured to:
 transmit, on each of the first transmit beam and one or more other transmit beams of the base station, multiple transmissions of the SSB corresponding to the first SSB type.   
     
     
         27 . The base station of  claim 24 , wherein the PRACH communication includes a PRACH preamble that indicates the first transmit beam of the base station and a beam from the RIS associated with a transmission of the SSB, of the multiple transmissions of the SSB, that is received by the UE. 
     
     
         28 . The base station of  claim 24 , wherein the RACH occasion during which the PRACH communication is received corresponds to the first transmit beam of the base station and a beam from the RIS associated with a transmission of the SSB, of the multiple transmissions of the SSB, that is received by the UE. 
     
     
         29 . The base station of  claim 24 , wherein the multiple PRACH transmission slots of the RACH occasion are associated with multiple transmissions of the PRACH communication by the UE, and wherein performing beam sweeping using the multiple receive beams of the base station comprises:
 monitoring each of the multiple PRACH transmission slots using a respective receive beam of the multiple receive beams base station to determine whether the PRACH communication is received on the respective receive beam.   
     
     
         30 . The base station of  claim 24 , wherein the first transmit beam corresponds to a first spatial filter of the base station and the first receive beam corresponds to a second spatial filter of the base station.